￥19 链表的删除￥删除链表的倒数第N个节点

不使用哑结点

100.00%
99%
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
   public static ListNode removeNthFromEnd(ListNode head, int n) {
        //统计head的长度
        ListNode q=new ListNode();
        ListNode p = head;
        int count=0;
        //计算长度
        while(p!=null){
            p=p.next;
            count++;
        }
        //控制n在1和count之间
       // if(n>=1&&n<=count){
            //删除head,且链表非空，，，，，1 <= count <= 30
            if(n==count&&count>1){
                head=head.next;
                return head;
            }
            if(n==count&&count==1){
                head=head.next;
                return head;
            }
            //不会删到头，返回head
            if(n<count){
                ListNode p1 = head;
                int count0=0;
                while(p1!=null){

                    count0=count0+1;

                    if(count0==count-n) {
                        p1.next = p1.next.next;
                        break;
                    }

                    p1=p1.next;
                }
                return head;
            }

    // }
return q;
     }
}

使用哑结点：链接：https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list/solution/shan-chu-lian-biao-de-dao-shu-di-nge-jie-dian-b-61/

class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(0, head);
        int length = getLength(head);
        ListNode cur = dummy;
        for (int i = 1; i < length - n + 1; ++i) {
            cur = cur.next;
        }
        cur.next = cur.next.next;
        ListNode ans = dummy.next;
        return ans;
    }

    public int getLength(ListNode head) {
        int length = 0;
        while (head != null) {
            ++length;
            head = head.next;
        }
        return length;
    }
}

作者：LeetCode-Solution
链接：https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list/solution/shan-chu-lian-biao-de-dao-shu-di-nge-jie-dian-b-61/
来源：力扣（LeetCode）
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